Doubts cast on claims that '19m Brits have had coronavirus'

Scientists have questioned a study that suggested that 25% of the UK have already had coronavirus. (Picture: PA)

Scientists have cast doubt on suggestions that more than 19million Britons have already had coronavirus.

A study by researchers from The University of Manchester, Salford Royal and Res Consortium, suggested that 29% of the population - more than 19m people - may already have been infected with COVID-19 and recovered.

The study, published in the International Journal of Clinical Practice, claimed to be the first to use published local authority data to assess the cumulative impact of infection since the outbreak began.

Dr Konstantin Blyuss, Reader in Mathematics at the University of Sussex, said: “There are several problems with this study.”

The first involves the data used, Dr Blyuss said, which only covers the period up to April 23 and suggests that the peak happened on April 8 and numbers of new cases had been below 4,000 since then, when in fact they had exceeded 4,000 for most of April and the first week of May.

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Another issue is that the study based its estimates on 73,000 reported cases, he said, while that number now stands at 233,000.

“The second issue concerns the methodology,” Dr Blyuss added. “The value of R is notoriously difficult to estimate, and as a result, the estimates always have a wide margin of error, which means that it is almost impossible to rely on accurate estimates of R for any significant population-wide conclusions.”

The results of the study were used in a front page story by the Daily Mirror on Friday. (Twitter)

Dr Adam Kucharski, Associate Professor in Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, also cast doubt on the study, saying: “In the absence of direct measurements, models can be useful for estimating the extent of infection from wider data sources.

“However, given how difficult it is to estimate the extent of unreported cases in a population from reported cases alone, it is likely that there is huge uncertainty in the estimates produced by the model used in this paper, and unfortunately this uncertainty is not reflected in the single value quoted in the paper and the press release.”

In the study, the researchers claimed that published local authority data had enabled them to calculate the R-value - the number of people infected by one person with COVID-19 - within each local authority area.

Dr Adrian Heald, from The University of Manchester, said: “COVID-19 is a highly infectious condition and very dangerous for a small group of people. However a much larger group seem to have low or no symptoms and have been unreported.

“This study tries to provide an estimate of the number of historic infections – and gives us all a glimmer of hope that there may be light at the end of the tunnel.

“We show how effective social distancing and lockdown has been. Though this is a tragedy, it could have been far worse”.

Mike Stedman from Res Consortium, who carried out the data analysis, added: “The figures are not perfect, with the numbers of severely ill patients as a proportion of the total cases being used as a market for estimates of wider infection.

“Only extensive antibody testing could give us a more accurate picture - but as that is only just becoming available, we believe this form of modelling is important in informing the best approach to unlocking the population.”